refactor: remove showFile API for Docker compatibility

Docker 容器内无法调用宿主机文件管理器，移除 showFile 接口：
- 移除后端 showFile 路由和处理函数
- 移除前端 showFile 调用和"打开文件位置"按钮
- 移除 opening 状态和 FolderSVG 组件

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/router/task.go

@@ -4,8 +4,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
-	"os/exec"
-	"runtime"
 	"strconv"
 	"time"
 
@@ -139,39 +137,6 @@ func getTaskList(w http.ResponseWriter, r *http.Request) {
 	util.Res{Success: true, Message: "获取成功", Data: tasks}.Write(w)
 }
 
-// showFile 调用 Explorer 查看文件位置
-func showFile(w http.ResponseWriter, r *http.Request) {
-	if err := r.ParseForm(); err != nil {
-		util.Res{Success: false, Message: "参数错误"}.Write(w)
-		return
-	}
-	filePath := r.FormValue("filePath")
-
-	var cmd *exec.Cmd
-
-	// 根据操作系统选择命令
-	switch runtime.GOOS {
-	case "windows":
-		// Windows 使用 explorer
-		cmd = exec.Command("explorer", "/select,", filePath)
-	case "darwin":
-		// macOS 使用 open
-		cmd = exec.Command("open", "-R", filePath)
-	case "linux":
-		// Linux 使用 xdg-open
-		cmd = exec.Command("xdg-open", filePath)
-	default:
-		util.Res{Success: false, Message: "不支持的操作系统"}.Write(w)
-		return
-	}
-	err := cmd.Start()
-	if err != nil {
-		util.Res{Success: false, Message: err.Error()}.Write(w)
-		return
-	}
-	util.Res{Success: true, Message: "操作成功"}.Write(w)
-}
-
 func deleteTask(w http.ResponseWriter, r *http.Request) {
 	// 支持单个删除（GET 参数 id）和批量删除（POST 参数 ids）
 	var taskIDs []int